1. Field of the Invention
The invention relates to a process for preparing high gloss laminated panels, the resulting high gloss laminated panels, to a resin composition for use in said process and a process for the manufacture of said resin composition.
2. Description of the Related Art
Laminated panels are typically manufactured by laminating a resin impregnated paper layer onto a substrate layer, for example high-density fiberboard (HDF), medium density fiberboard (MDF) or particle board. The resin impregnated paper layer is provided to mainly decorate the substrate layer and desirably to form a smooth, glossy and durable surface layer.
A surface can generally be classified as high gloss when 70 gloss units are measured according to standard EN 14323:2004. The industry still considers high-pressure lamination (HPL) as the benchmark requirement for obtaining high gloss laminate surfaces (above 110 gloss units). With current melamine formaldehyde (MF) resins a high gloss (above 110) and non orange peel surface cannot be achieved by standard direct pressed laminates (DPL) process technology. HPL itself is expensive and the manufacture of HPL is labour intensive and time consuming. The gloss is measured using a standard gloss meter according to ISO 2813 as described in EN 14323 section 5.13.
The reasons why DPL cannot deliver high gloss surfaces using MF resins are manifold. For example, typically the press is opened hot after pressing and the water steam which has been liberated by the condensation of the resin (from B stage in the paper to C stage in the surfacing layer) evaporates immediately thus destroying the smooth and glossy surface. This can of course be avoided, and it is known in the industry to do so, by a so called back cooling step in which the press is cooled to lower than water boiling point temperatures prior to opening but this self evidently reduces the output of the process. DPL technology as described here is nevertheless currently commercially applied by e.g. FunderMax (St. Veit/Glan, Austria).
It was found that, although MF resins are generally considered to have no flow, the resin still flows at a very limited level. The resin is flowing both in DPL and HPL from the impregnated paper into the substrate. Due to this, the typically very thin surfacing MF layer, which is responsible for achieving a good gloss level, decreases its thickness even further, enabling paper fibers come through the surfacing MF thus reducing the very high gloss. To help this somewhat, there are many bypasses used. One is to increase the resin content to a very high level which makes it cost wise unattractive. Kaindl WO 2006119950A1 describes to use densified, smoothened papers to achieve a thicker and smoother MF resin surfacing layer without drastically increasing the total resin content.
Another solution applied to both DPL and HPL could theoretically be to adjust the reactivity of the impregnation formulation at a very fast level, optionally combined with a very low volatile content of the impregnated paper which together helps a faster curing in the press and thus reducing the flow and the total amount of liberated water. Another solution could be to use cooling when press is cooled, so as to minimize the release of water, known as back cooling. Furthermore, a high degree of condensation in the resin formulation is favorable but this reduces the shelf life of the resin for the same reasons. However, all these measures together nevertheless make only a limited medium gloss level possible and high gloss is still out of reach.
Thus, there is a particular need for a process for manufacturing high gloss laminated panels, in particular there is a need for a resin composition for use in that process that at comparable solids contents and degree of condensation can provide high gloss laminated panels even in a direct pressing laminate (DPL) processes without a need for a back cooling process.